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Comparative analysis of detection methods for Asian soybean rust.

Presenter: Philip F. Harmon, UF/IFAS, Department of Plant Pathology
Coauthor(s): Carrie L. Harmon / UF/IFAS, Department of Plant Pathology and the Southern Plant Diagnostic Network

Asian soybean rust caused by Phakopsora pachyrhizi was first diagnosed on soybean in the continental US in fall 2004. Many consultants, producers, county and state faculty, and diagnosticians have been trained to recognize signs and symptoms of this disease and to submit suspect samples to a diagnostic laboratory for confirmation. In this study, three diagnostic protocols were evaluated at six university plant disease laboratories for timeliness and reliability of results. In five of the six locations, samples were selected for this study from those submitted to the respective diagnostic laboratory. In Florida, however, 30 species and varieties of bean were established in 3 plantings within 3.2 miles of a known-positive kudzu site. Suspect Florida samples were selected from the variety trial and from the known-positive kudzu site through weekly scouting, in addition to samples submitted through normal channels. Combined, samples from all labs included leaf tissue of four leguminous hosts, the majority of which were Glycine max (81%). Samples were characterized as presumed positive or presumed negative after observation under the dissecting microscope for uredinia and urediniospores consistent with P. pachyrhizi. Ten presumed negative samples and, where available, ten presumed positive samples were processed by each lab in triplicate using a commercial ELISA plate kit and one of the PCR protocols from the literature. Time required to process each sample and the consistency of results produced with each method are reported.

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